The present invention generally relates to a solder composition and to a method for making a solder composition having a relatively long shelf life, a desired melting temperature, an d which uses en vironmentally desirable materials.
Solder compositions are used to selectively attach electrical and electronic components (collectively referred to as xe2x80x9cthe componentsxe2x80x9d) to a circuit board or module. Typically, the solder composition is mixed with a flux and a carrier material to cooperatively form a solder paste. The solder paste is selectively deposited upon the solder pad portions of the various electronic circuits which are operatively contained upon and/or which are formed within these circuit boards or modules and the components are selectively and respectively placed upon these various solder deposits. The solder containing assemblies are then transported through an oven and are heated, effective to cause the flux to become activated and to remove oxide materials which may be present upon the pads and/or components. The solder material then melts, flows, and metallurgically interacts with the solder pads and the components. As the solder material cools, electrical interconnections are formed between the various components and the circuits, thereby allowing the various circuits and modules to perform their respectively desired functions.
Many of the prior solder compositions include material, such as lead, which is environmentally undesirable. While some attempts have been made to provide solder compositions without the use of lead, these solder compositions have a relatively high melting temperature, therefore requiring a soldering temperature which cause undesirable damage or destruction to the components and/or to the circuit board and module, or have a melting temperature that is undesirably low and which causes the solder, of a formed joint, to xe2x80x9ccreepxe2x80x9d and/or xe2x80x9ccrackxe2x80x9d during normal operation. Further, these compositions have a relatively short xe2x80x9cshelf lifexe2x80x9d (i.e., they require use shortly after being created), thereby complicating the soldering process, undesirably increasing the overall soldering cost, and restricting their respective use in large volume production type operations. Further, these prior xe2x80x9cnon-leadedxe2x80x9d soldering compositions do not generally provide robust joints without the use of flux material which undesirably requires the use of known ozone depleting cleaning agents to clean the module after soldering in order to substantially prevent the formation of flux residues which undesirably cause malfunction of the circuit board or module.
There is therefore a need for a xe2x80x9cnon-leadedxe2x80x9d or xe2x80x9cenvironmentally friendlyxe2x80x9d solder composition which overcomes at least some of the previously delineated drawbacks of prior non-leaded solder compositions and which, by way of example and without limitation, allows for the selective formation of generally reliable joints and which has a melting temperature which is substantially similar to the melting temperature of many xe2x80x9clead basedxe2x80x9d solder compositions which are already in use in current production, such that minimal changes will be required to utilize this new and useful solder composition in these operations (i.e., the new and improved solder composition may function as a xe2x80x9cdrop inxe2x80x9d replacement for currently used lead based solder compositions).
It is a first object of the present invention to provide a solder composition and a method for making such a solder composition which overcomes many of the drawbacks of prior solder compositions.
It is a second object of the present invention to provide a solder composition and a method for making such a solder composition which overcomes many of the drawbacks of prior solder compositions and which is comprised of tin and zinc, thereby obviating the need for lead material.
It is a third object of the present invention to provide a non-leaded solder composition which has a melting temperature which is substantially similar to the melting temperature of many lead based solder compositions which are currently used in large volume production.
It is a fourth object of the present invention to provide a non-leaded solder composition which has a relatively long shelf life and which has a melting temperature which is substantially similar to prior lead based solder compositions.
According to a first aspect of the present invention, a solder composition is provided. The solder composition includes an alloy of tin and zinc wherein at least a portion of the zinc is coated with tin.
According to a second aspect of the present invention, a method for creating a solder composition is provided. The method comprises the steps of forming a first material; then forming a thin layer of tin upon at least a portion of the first material.
These and other features, aspects, and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.